1. Field of the Invention
The present invention relates to a method of producing ceramics base plates and specifically to a method of obtaining ceramics base plates by dividing a large ceramics sintered base plate. Also, the invention relates to a ceramics base plate obtained by the method.
2. Description of the Related Art
Hitherto, as methods of dividing a ceramics sintered base plate into plural ceramics base plates dicing with a cutting blade containing grinding stone particles such as diamond, etc. and cutting with laser beams have been generally known. In these methods, in addition to the case of completely A cutting a ceramics sintered base plate, dividing a ceramics sintered-base-plate by applying an external force after half cutting the base plate is also carried out.
Dicing with a cutting blade is most generally carried out. For example, the ceramics sintered base plate is cut while relatively moving the base plate to the X direction and/or the Y direction to the cutting blade. Of the dicing methods, a method of dividing a ceramics sintered base plate by applying an external force after half cutting the base plate to a definite depth enables the restraint of the processing cost as compared with the case of completely cutting by reasons such as high treatment capacity, low abrasion of the cutting blade, etc.
Also, in the case of cutting with laser beams, in general, fine holes are continuously formed in a ceramics sintered base plate upon irradiation with laser beams in a dot-like form. When the formed fine holes penetrate through the ceramics sintered base plate, the ceramics sintered base plate is completely divided at a stretch. On the other hand, when the fine holes do not penetrate through the ceramics sintered base plate, the cutting is of half cutting, and the base plate is then divided by applying an external force. Even in this case, the method of dividing the ceramics sintered base plate after half cutting enables the restraint of the processing cost because the treatment time is generally short as compared with the case of completely dividing the base plate.
In addition, there is also a method, though not so wide spread, in which half cutting is applied to a molding of a ceramics, and the molding is sintered to form a ceramics sintered base plate, which is then divided along the half cut portion.
Of the related art methods as described above, as shown in FIG. 3, in the case of cutting a ceramics sintered base plate 1 by dicing using a cutting blade 3, a portion of the ceramics corresponding to a blade width d of the cutting blade 3 is wasted as swarf. Also, since the abrasion of the cutting blade 3 is severe, diamond is frequently used for the cutting blade. Under such circumstances, in dicing using the cutting blade 3, the drawback is that the processing cost is increased.
Furthermore, in the general method of dividing a ceramics base plate along the half cut groove after half cutting by dicing using a cutting blade 3, because each ceramics base plate 2 obtained by dividing has cut residual portions 2a by half cutting as shown in FIG. 4, a deviation in size is generated corresponding to two times, at the largest, the blade width d of the cutting blade 3 to the desired base plate size D. Also, when the cut residual portions 2a remain on the ceramics base plate 2, there exist many portions which could become a breakage-starting point, resulting in a fault of relatively lowered breaking strength of the ceramics base plate 2.
Also, in the case of dicing with a cutting blade, a cooling medium such as water is used to prevent heating of the cutting blade or the ceramics art sintered base plate during cutting. If the ceramics sintered base plate is made of aluminum nitride, when the base plate is allowed to stand with water, there is a problem of the generation of ammonia.
On the other hand, because in the case of cutting with laser beams, fine holes are formed upon irradiation with laser beams, even when cutting is of complete cutting or half cutting, a trace by the irradiation with laser beams remains on the obtained ceramics base plate. The trace portion formed by the irradiation with laser beams becomes a breakage-starting point, whereby the strength of the divided ceramics base plates is liable to be lowered. Also, when the heat conductivity of a ceramics base plate is high, the heat by the irradiated laser beams diffuses on the base plate. Therefore, a treatment of prolonging the time for irradiation with laser beams or of increasing the output of laser beams is necessary, resulting in a problem of an increase in the processing cost.
Further, when laser beams are irradiated, the ceramics components, which have not been sublimed completely, attach or weld to the peripheral portions of the fine holes formed by the laser. Because these attached or welded substances are present in a convex form on the ceramics base plate, when, for example, a paste is screen-printed in case of forming a metallized layer of a baking type, defects may occur on the printed pattern or the metallized layer after baking and these attached substances damage the printed pattern, and may possibly result in the breakage of the screen.
In case of the method of applying half cutting to the molding and dividing it after sintering, the dimensional accuracy is lowered, as the size of a ceramics base plate increases, because of a dispersion shrinkage by sintering.